Failure to recognize incipient and emerging dehydration or overhydration leads to adverse outcomes. Potentially life-threatening dehydration occurs frequently. Though less often, serious overhydration also occurs, usually in connection with chronic conditions such as renal disease and dialysis or congestive heart failure. In children, dehydration often leads to unplanned visits to Emergency Departments. In the elderly living in their own homes, significant dehydration often occurs without the person being aware of it; eventually, hypovolemia or electrolyte abnormalities associated with dehydration lead to a state of diminished cardiac output or hypotension, resulting in syncope and falling. In long-term care facilities, dehydration often leads to transfer to a hospital or other acute-care facility and sometimes leads to death.